The present disclosure relates generally to heated glass temperature-controlled storage device and more particularly to a controller, system, and method for trimming power used by a heated glass temperature-controlled storage device.
Heated glass temperature-controlled storage devices (e.g., refrigerators, freezers, refrigerated merchandisers, etc.) are used in a wide variety of commercial, institutional, and residential applications for storing and/or displaying refrigerated or frozen items. For example, self-service type refrigerated display cases or merchandisers are often used in grocery stores, supermarkets, convenience stores, florist shops, and other commercial settings to store and display the temperature-sensitive consumer goods (e.g., food products and the like).
Many heated glass temperature-controlled storage device have a glass door through which items within the heated glass temperature-controlled storage device may be viewed. A heated glass temperature-controlled storage device often includes heaters in the glass door and the door frame to prevent condensation from forming on and around the glass of the storage device.
Since glass is a conducting material, the glass doors of heated glass temperature-controlled storage devices are commonly coated with a resistive material to which is applied a current to heat the material and thereby the glass. The resistive material has a standard impedance, and the impedance of glass coated with the resistive material depends in part on the standard impedance, thickness of the coating, and size of the glass. When a current is applied, the power used is generated as heat, where the amount of heat generated depends on the applied current. A number of factors determine how much heat is necessary to prevent or eliminate condensation, including the ambient environment and size of the glass. For instance, a heated glass temperature-controlled storage device used in a humid environment would require more heat than would a heated glass temperature-controlled storage device used in an arid environment. Therefore, the glass of a heated glass temperature-controlled storage device for a humid area optimally should be coated with less material than one for an arid area. Coating of resistive material often is done in certain standard amounts, without allowing for particular resistive values. This leads to situations where the amount of power used by a heated glass temperature-controlled storage device is greater than a minimum amount necessary to prevent condensation. This gives rise to a need for a means for applying a proper current to a glass heater circuit which may have a predetermined resistive value, and may be used in environments with varying humidity and temperature. There is a need for a reliable, low-cost, and predictable method of applying current to the resistive material on such heated glass temperature-controlled storage device to limit the power used to be within a predetermined value.